From fe28cdbd1f31c35f68f95d8a1a38edb30960eb43 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 27 Nov 2022 19:50:49 +0200
Subject: [PATCH] Add boost::hash_value for std::nullptr_t. Refs #29.

---
 include/boost/container_hash/hash.hpp | 14 +++++++++
 test/Jamfile.v2                       |  2 ++
 test/hash_nullptr_test.cpp            | 41 +++++++++++++++++++++++++++
 3 files changed, 57 insertions(+)
 create mode 100644 test/hash_nullptr_test.cpp

diff --git a/include/boost/container_hash/hash.hpp b/include/boost/container_hash/hash.hpp
index 306c279..10eb18a 100644
--- a/include/boost/container_hash/hash.hpp
+++ b/include/boost/container_hash/hash.hpp
@@ -27,6 +27,7 @@
 #include <boost/type_traits/enable_if.hpp>
 #include <boost/type_traits/conjunction.hpp>
 #include <boost/type_traits/is_union.hpp>
+#include <boost/type_traits/is_same.hpp>
 #include <boost/describe/bases.hpp>
 #include <boost/describe/members.hpp>
 #include <boost/cstdint.hpp>
@@ -494,6 +495,19 @@ namespace boost
         return seed;
     }
 
+#endif
+
+    // std::nullptr_t
+
+#if !defined(BOOST_NO_CXX11_NULLPTR)
+
+    template <typename T>
+    typename boost::enable_if_<boost::is_same<T, std::nullptr_t>::value, std::size_t>::type
+        hash_value( T const& v )
+    {
+        return boost::hash_value( static_cast<void*>( v ) );
+    }
+
 #endif
 
     // std::optional
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index b5985cc..7b2eccc 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -115,3 +115,5 @@ run described_class_test.cpp
 
 run hash_is_avalanching_test.cpp ;
 run hash_is_avalanching_test2.cpp ;
+
+run hash_nullptr_test.cpp ;
diff --git a/test/hash_nullptr_test.cpp b/test/hash_nullptr_test.cpp
new file mode 100644
index 0000000..05a921c
--- /dev/null
+++ b/test/hash_nullptr_test.cpp
@@ -0,0 +1,41 @@
+// Copyright 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/container_hash/hash.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <cstddef>
+
+#if defined(BOOST_NO_CXX11_NULLPTR)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped, BOOST_NO_CXX11_NULLPTR is defined" )
+int main() {}
+
+#else
+
+template<class T> std::size_t hv( T const& x )
+{
+    return boost::hash<T>()( x );
+}
+
+int main()
+{
+    {
+        BOOST_TEST_EQ( hv((void*)0), hv(nullptr) );
+    }
+
+    {
+        int x = 0;
+
+        BOOST_TEST_EQ( hv((int*)0), hv(nullptr) );
+        BOOST_TEST_NE( hv(&x), hv(nullptr) );
+
+        (void)x;
+    }
+
+    return boost::report_errors();
+}
+
+#endif